Detection system for superposed sheets

ABSTRACT

A multiple sheet detecting system for use in a sheet feed path to provide a signal to a machine control when superposed sheets are fed past a detection station. The detection system has a source of illumination and photosensitive elements at the detection station. Illumination is interrupted by the presence of a sheet or sheets in the sheet path and also by a sample sheet such that a comparison is made between the sample and fed sheets. An electronic circuit coupled to the photosensitive elements which experience a change in resistance depending upon the transmittance of a sheet or sheets in the sheet path generates an output signal when there is a multiple sheet condition. The circuit may be calibrated for varying circuit parameters to accommodate different sheet weights and types.

1451 May 6,1975

[ DETECTION SYSTEM FOR SUPERPOSED SHEETS [75] Inventors: John W. Daughton, Fairport; Gary L. Schluntz, Penfield, both of NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Apr. 6, 1970 [21] Appl. No.: 25,804

52 us. 01. 250/222 R; 356/206 51 1111.01. H0lj 39/12 581 Field ofSearch..... 250/221, 222,223, 219 DC, 250/29 F, 83.3 1), 218, 219 R, 219 or, 219

TH; 235/61.11 E; 178/42; 340/259; 356/204,

[56] References Cited UNITED STATES PATENTS 2,512,247 6/1950 Fua 250/833 D 2,517,330 8/1950 Marenholtz 2,646,556 7/1953 Allen 3,026,419 3/l962 Aweida 250/219 DC 3,372,276 3/1968 Reynolds 250/833 D Primary Examiner-James W. Lawrence Assistant Examiner-D. C. Nelms [57] ABSTRACT A multiple sheet detecting system for use in a sheet feed path to provide a signal to a machine control when superposed sheets are fed past a detection station. The detection system has a source of illumination and photosensitive elements at the detection station. Illumination is interrupted by the presence of a sheet or sheets in the sheet path and also by a sample sheet such that a comparison is made between the sample and fed sheets. An electronic circuit coupled to the photosensitive elements which experience a change in resistance depending upon the transmittance of a sheet or sheets in the sheet path generates an output signal when there is a multiple sheet condition. The circuit may be calibrated for varying circuit parameters to accommodate different sheet weights and types.

1 Claim, 5 Drawing Figures PATENTEDNAY ems 3.882.308

SHEET 1 0F 4 INVENTORS JOHN W. DAUGHTON GARY L. SCHLUNTZ ATTOPNFV FATENTEDMAY ems 3,882,308

sum 2 or 4 IIIIAIIIIIIIIIIIIII Ill/l FIG. 2A

PATENTEWAT 6 I975 SHEET R 0F 4 mwnn .Euxm mjuzm f v at All! NEE.

mFWmIm MJmEHSE DETECTION SYSTEM FOR SUPERPOSED SHEETS This invention relates to a multiple sheet detection system to detect the presence of superposed sheets advanced along a sheet path and to indicate to a machine control that a multiple sheet feed condition has occurred.

In feeding copy sheet material along a path, for ex ample, through a copy processor, it is essential to ad vance one sheet at a time and to prevent the forwarding of multiple or superposed sheets. When multiple sheets are forwarded accidentally, jams occur at the process ing stations which result in a machine malfunction. With the advent of high speed reproduction machines incorporating complex sheet feed systems feeding different sheet sizes, weights, etc., problems associated with multiple sheets have become increasingly apparent.

Usually the detection of multiple or superposed sheets is accomplished by mechanical sensors as described, for example, in US. Pat. No. 3,396,965. While these devices are suitable in somecases, they are not entirely satisfactory in many present day reproduction systems.

It is therefore the principal object of this invention to improve multiple sheet detection systems.

It is another object of the present invention to enable detection of superposed sheets fed in a sheet path and to indicate this condition to a machine control irrespective of the weight or thickness of the sheet stock being fed.

It is another object of the invention to enable detection of multiple sheets being fed past a detection station at very high rates. 1

It is another object of the invention to detect the feeding of multiple sheets by measuring the light transmission of sheet material and sensing differences in the transmission of sheets being fed and a reference transmission provided by a sample sheet.

It is another object of the present invention to utilize electronic circuitry to determine when multiple sheets are being fed along a sheet path.

It is another object of the present invention to facilitate the detection of superposed sheets being fed along a sheet path in a manner more simple and more rapid than that used heretofore.

The detection system of the invention, generally speaking, is accomplished by comparing the light transmittance of each fed sheet with that of a sample sheet and utilizing an electronic circuit for comparing differences of the transmissions and generating appropriate signals to machine control to indicate the presence of superposed sheets.

For a better understanding of the invention as well as other objects and features thereof, reference is had to the following detailed description of the invention which is to be read in connection with the accompanying drawings wherein:

FIG. 1 illustrates schematically a xerographic record ing apparatus incorporating a multiple sheet detection system constructed in accordance with the present invention;

FIG. 2 is an enlarged view of the sheet detection station of the apparatus illustrating the illumination assembly and the detector photosensor assembly of the present invention and their relationship to the sheet feed path;

FIG. 2A is a partial end view of the detection station of FIG. 2 illustrating details of the illumination assembly and the detector and sample sheet photosensor assemblies;

FIG. 3 is a circuit diagram of the multiple sheet detection system; and v FIG. 4 is a diagram illustrating signal voltage variations indicative of single and multiple sheet feed conditions.

Referring now to FIG. 1, there is shown various components of a xerographic recording machine which produces enlarged copies of microfilm aperture cards on cut sheets of different sizes and weights at high rates and which utilizes a multiple sheet detection system according to the present invention. As in all xerographic recording systems, a light image of an original to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a powder image corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface such as paper to which it is permanently affixed.

In the recording machine of FIG. 1, aperture cards are placed in a card feed section 16 from which each card is fed in seriatim in a path transverse to the optical path to scan a film frame on the card in timed relation to the movement of a xerographic plate which is in the form of a drum 20. Xerographic drum 20 comprises a layer of photoconductive material on a conductive backing and is mounted in suitable bearings in a machine frame and driven by a suitable drive. The drum passes first a charging station A at which a uniform electrostatic charge is deposited by a corona generating device 21. Next, at an exposure station B, the drum is exposed to a light image to discharge the photoconductive layer in the areas struck by light whereby there remains on the drum a latent electrostatic image corresponding to the film frame on the aperture card being scanned. As the drum continues its movement, the electrostatic latent image passes through a development station C at which a developing material including toner particles having electrostatic charge opposite to that of the electrostatic latent image are cascaded across the drum surface whereby the toner particles adhere to the latent image to form a powdered image. As toner powder images are formed, additional toner particles are supplied to the developing material in proportion to the amount of toner deposited on the drum. Positioned adjacent to the development station C is an image transfer station D at which the powder images are electrostatically transferred from the drum surface to sheet material supplied from a sheet feed station past a sheet detection station in a manner as will be explained more fully hereinafter.

A sheet transport apparatus, generally designated 25, serves to transport the sheet material received from a sheet feed section 27 toward a transfer station D where a corona transfer device 29 similar to the corona charging device 21 is located to affect the electrostatic transfer of the developed image onto the sheet material. After transfer, the powder image is permanently affixed to the sheet material by a heat fuser apparatus 31 and the sheet material conveyed onto a vertical transport 33 for delivery to a copy tray 35. A drum cleaning station E comprises a corona discharge device 37 and brush 39 to remove residual toner particles remaining on the drum surface after image transfer, and a light source 40 to complete discharge of any residual electrostatic charge remaining on the surface whereby the drum may be ready for another cycle to pass through the processing stations as just described.

It is believed that the foregoing description of the Xerographic recording apparatus is sufficient for purposes of showing a general operation of a typical recording apparatus using a multiple sheet detection system constructed in accordance with the present invention. For further details concerning the specific construction of the xerographic machine components previously described, reference is made to copending applications Ser. No. 824,541 filed on May 14, 1969, entitled Multiple Output Electrostatic Recording System; and Ser. No. 824,542 filed on May 14, 1969, entitled Copier Machine Feeding Multiple Size Copy Sheets. It should be understood. however, that the detection system of the present invention is not limited to use in copier machines and may find use in many suitable environments.

In FIG. 2, there is shown a sheet detection station located at the exit side of sheet feed section 27 which feeds sheets of different sizes and/or types as selected from a conveniently located control panel. Sheets are fed desirably one at a time toward guide members 45 which converge and terminate at the exit of the sheet feed sections where the multiple sheet detection station is positioned. It will be appreciated that the sheet feed section is modular and is of the type which can be easily pulled away from the rest of the xerographic recording machine as described more fully in the previously mentioned copending applications.

At the multiple sheet detection station, there is positioned an illumination assembly 51 situated below the sheet feed path and a pair of photosensor assemblies 53 and 55. Photosensor assembly 53 is located just above the sheet path while photosensor assembly 55 is mounted below the sheet path for comparing fed sheets with a sample sheet as will become more apparent. I1- lumination assembly 51 includes a source of illumination DSl which may be an incandescent lamp or other suitable light source in a housing 57 formed with an aperture 59 and an aperture 61 such that illumination can be sensed in two directions (FIG. 2A). A photosensitive element V1 receives illumination through an aperture 62 located in a housing 63 and photosensitive element V2 receives illumination through an aperture 64 in a housing 65. Photosensitive elements V1 and V2 may be any suitable light sensitive device. Typically the photosensitive element may include a photocell, photovoltaic, photoconductor, phototransistor, photodiode, etc. It is preferred to use a cadmium sulfide or cadmium selenide photocell due to their increased sensitivity. Guide members 45 are notched or opened to provide an uninterrupted flow of illumination in a direction across the sheet path. Mounted on housing 57 is a leaf spring member 66 which is adapted to hold a smaple sheet portion S in overlying relation to aperture 61 (FIG. 2A). Source ofillumination D51 is adjustable relative to the housing as by screws 67 received in the housing against the action of springs 68. It will be appreciated that the overall configuration of the source of illumination and its apertures and the photosensitive elements and their apertures is such that any variation in sensitivity due to differences in the sheet path is minimized.

In accordance with the invention as a sheet advances past the source of illumination and photosensor assemblies, illumination from DSl is interrupted in the direction of photosensitive element V1 which causes an increase in the resistance of this element while photosensitive element V2 remains unaffected. The photosensitive elements are coupled to an electronic circuit which produces an output signal to machine control as will be described hereinafter. The photosensitive element resistance level normally generated by advancing single sheets is such as to be the same or nearly the same as the light transmission of sample sheet portion S. However, when superposed or multiple sheets are fed past the detection station, the drop in light transmission causes the resistance of photosensitive element V1 to increase significantly above that of V2. When this occurs, the electronic circuit coupled to the photosensitive elements utilizes this resistance change to generate an output signal to a machine control to indicate the presence of multiple sheets.

A better understanding of the invention may be had in connection with the circuit illustrated in FIG. 3. The circuit has a regulated, well filtered power supply which is made up of a transformer T1, bridge rectifier CR1, resistors R1, R2 and R3, capacitors C1 and C2 and zener diodes CR2 and CR3. It has been found that output voltages from such a power supply of about plus and minus 12 volts performs well for purposes of the present invention. Transformer T1 also provides a supply voltage for source of illumination DSl. A resistor R11 is used to provide an unfiltered power source for a relay Kl which is energized in a manner to be described hereinafter. Photosensitive element V1, a trim pot R6 and a resistor R7 serve to make up a voltage divider for sensing. To initially calibrate the circuit, a single sheet is positioned at the detection station and trim pot R6 is adjusted to establish a voltage at point A of about one half the normal supply voltage which in this case is 6 volts. In similar fashion, photosensitive element V2, a trim pot R14, a trim pot R4 and a potentiometer R36 make up a voltage divider which generates an output representative of the light transmittance of sample sheet portion S.

It will be noted that a resistor R15 provides a low resistance path around photosensitive element V2, trim pot R4, and potentiometer R36. By this arrangement, it is possible to establish a suitable reference voltage at point B when a sample sheet portion S is in operating position and with potentiometer R36 set at its center of rotation by adjusting variable resistor R4. When this is accomplished, trim pot R14 is adjusted to establish a suitable offset voltage y between point C and point D. Offset voltage y should not be too low so that a dense single sheet will actuate the detection system to indicate a double sheet condition or so high that very light or high transmittance superposed sheets being fed past the detecting station do not indicate a single sheet condition. For a supply of 12 volts, it has been found that an offset voltage y is desirable which ranges from about 0.5 volts to about 2 volts and preferably about 1.2 volts (FIG. 4).

It will be noted that point A is connected to the negative input of a differential amplifier Q1. It will be further noted that point B is connected to the positive input of differential amplifier Q1. When point B goes positive with respect to point A, Q] will be turned on which in turn will cause transistor G2 to turn on which drives a relay Kl coupled to machine control. It will now be appreciated that the voltage at point B goes positive with respect to the voltage at point A when a multiple sheet feed condition occurs at the sheet detection station causing Q1 and ()2 to be turned on and relay Kl to be actuated. Relay Kl energizes'a suitable indicator for the multiple sheet condition and/or deenergizes the machine processor before a malfunction can occur.

In order to accommodate great differences in weights and types of sheet material in the detection system of the invention, the system is adapted for calibration to meet such varying conditions. To accomplish this, a calibration switch S38 is provided to be manually actuated during the time that a single sheet of the material of the type to be fed is introduced at the detection station. Switch S38 is held actuated until such time as potentiometer R36 can be adjusted to turn on Q1 for the most dense sheet to be fed or when point B is about 1.2 volts negative with respect to point A. When this occurs, calibration is complete since the circuit previously described is adapted to turn on Q1 and Q2 and actuate relay Kl only when the transmittance indicates a multiple sheet condition is present. By this arrange ment, it is possible to use different types and weights of sheet material in a multiple sheet detection system.

In order to ensure reliable operation at all times, a resistor R and a zener diode CR4 are provided to indicate multiple sheets are present if illumination source DSl fails. By this arrangement, Q1 will turn on when illumination ceases thereby providing a fail-safe operation.

The invention described above enables multiple sheets to be detected in a rapid and simple manner without sacrificing reliability. The detection system is error free since a balanced condition is maintained in the circuitry despite aging of the illumination assembly or response of the photosensor assemblies. Thus, the detection system combines a stability of performance with speed of operation. Moreover, the great latitude of sheet weights and types that can be accommodated in the system of the invention is highly desirable. It will be appreciated that the sheet detection system of the invention is useful in environments such as the present day copier/duplicator machines.

What is claimed is:

l. [n a recording machine in which copy sheets are advanced through copy processing stations along a predetermined path, an improved detection apparatus for detecting multiple superposed sheets at a sheet detection station comprising means for feeding sheet material along a sheet path past copy processing stations.

illumination means positioned along the sheet path at a sheet detection station,

first photosensitive means for receiving illumination from said illumination means,

second photosensitive means for receiving illumination from said illumination means,

sample sheet material interposed between said illumination means and said second photosensitive means,

first circuit means for generating discrete electrical signals representative of the transmittance of sheet material to be detected,

second circuit means responsive to the transmittance of the sample sheet material for generating a signal representative of the transmittance of said sample sheet material,

third circuit means for comparing the signals generated from said first and second circuit means and determining the presence of multiple superposed sheets and generating an output signal to machine control to de-energize the machine when a multiple superposed sheet condition occurs at the sheet detection station, and

means for maintaining a multiple superposed sheet output condition in the event that a failure of said illumination means occurs. 

1. In a recording machine in which copy sheets are advanced through copy processing stations along a predetermined path, an improved detection apparatus for detecting multiple superposed sheets at a sheet detection station comprising means for feeding sheet material along a sheet path past copy processing stations, illumination means positioned along the sheet path at a sheet detection station, first photosensitive means for receiving illumination from said illumination means, second photosensitive means for receiving illumination from said illumination means, sample sheet material interposed between said illumination means and said second photosensitive means, first circuit means for generating discrete electrical signals representative of the transmittance of sheet material to be detected, second circuit means responsive to the transmittance of the sample sheet material for generating a signal representative of the transmittance of said sample sheet material, third circuit means for comparing the signals generated from said first and second circuit means and determining the presence of multiple superposed sheets and generating an output signal to machine control to de-energize the machine when a multiple superposed sheet condition occurs at the sheet detection station, and means for maintaining a multiple superposed sheet output condition in the event that a failure of said illumination means occurs. 